1. Field of the Invention
This invention relates to a method for repairing and restoring a deteriorated cement-containing inorganic material, typically reinforced concrete, according to which the repaired cement-containing inorganic material can be kept alkaline semipermanently.
2. Description of Prior Art
A reinforced concrete structure is a complex durable structure of cement concrete with reinforcements which are protected against rusting in a highly alkaline atmosphere in the concrete, but the concrete itself is carbonated by carbon dioxide in the air to cause rusting of the reinforcements over a long-time period. When the reinforcements are rusted, the covering concrete cracks due to the cubic expansion pressure, and oxygen and moisture enter from the cracks to promote rusting, thus causing scale-off of the covering concrete. As a result of the repetition of such an action, the reinforced concrete structure is badly impaired in its durability. Such a phenomenon may occur in short-time use if the structure is placed under certain environmental conditions. It is aggravated by fire or exposure to exhaust gas, and especially marine structures or structures located close to the seaside tend to suffer such damage early in use since the reinforcements of these structures are always exposed to a corrosive environment.
This phenomenon is observed not only in reinforced concrete but also in other inorganic materials containing cement. These materials are hardened and petrified in long-time use under various conditions. These cement-containing inorganic materials are most suited for general structures and buildings because of their excellent rigidity and durability, but they suffer such damage and aging gradually or even rapidly (in short-time use) under certain conditions not only due to the carbonating actions (which are caused and/or promoted not only by carbon dioxide in the air but also by exhaust gas, fire, etc.) but also under the influences of other factors such as penetration of water (including seawater and water containing acids, alkalis, salts, etc.) and oils, wear, cavitation, alkali-aggregate reactions, etc. Further, in the case of cement concrete, it usually inevitably suffers from cracking due to shrinkage on drying and other types of structural cracking, and if cracks are formed in such concrete, its waterproofness is degraded to let weathering such as carbonation of concrete advance deep into the inside thereof.
Thus, if such deterioration of quality or durability of a reinforced concrete structure or component inorganic material thereof, such as cement concrete is left unattended, the structure will turn into a dangerous state which may lead to a disaster. To avoid this, it is desirable to rebuild the structure, but due to the need to save material and energy in these years, repairing and restoring of the structure and its component material is now given serious consideration, and an advanced technique for such reparing and restoring of material is sought after in the field of civil engineering and construction, too.
Hitherto, repairing of a reinforced concrete structure has been made by applying an anti-corrosive paint such as zinc-rich paint or an epoxy resin to the exposed reinforcements, or the damaged section has been tentatively repaired by injecting an epoxy resin or the like into the cracked portion of the concrete, since no effective alkalinity recovery method was available for the repairment of the carbonated portion of the concrete. However, zinc-rich paint is unable to protect the alkali in the concrete in a satisfactory way, while the epoxy resin has problems not only in workability and economy but also, more importantly, in durability since it is an organic compound. In the use of the epoxy resin for repair of marine structures, a case is reported where corrosion of the inside reinforcements started again in about one year after the repair work. Therefore, in view of the durability after the repair work, it is desirable to use an inorganic compound as the repairing material for the reinforced concrete structures. On the other hand, utilization of a special colloidal silica prepared by combining an alkali metal silicate and an ammonium silicate compound has been studied for preventing surface deterioration of inorganic material (Japanese Patent Publication No. 19609/1978). However, although such a colloidal silica has excellent water and weather resistance, it is poor in its ability to recover alkalinity in the carbonated portion of the concrete because of a high molar ratio of SiO.sub.2 and a low alkalinity. Also, since such a colloidal silica is composed of colloidal particles, its penetrability into the inside of concrete is lower than that of watersoluble compounds.
Surface reinforcement of the inorganic material by impregnation with a water-soluble silicate compound is also considered, but such a compound tends to be eluted to lose its effect in long-time use because of its poor water resistance after curing. Also, mere coating with cement paste alone or together with a high polymer dispersion or mere mortar grouting on the scaled-off portion of concrete is unsatisfactory for reinforcing the concrete body or for preventing corrosion of the reinforcements by recovery of alkalinity because of poor penetrability into the inside of the aged or deteriorated concrete.
Thus, a means for realizing recovery of alkalinity in the inside carbonated portion of concrete and its surface reinforcement by impregnation with a water-soluble silicate compound and at the same time the development of a topcoat (with cement paste or mortar) for preventing elution of the water-soluble silicate compound have been keenly required.